1. Field of the Invention
This invention relates to a container for aerobically composting organic waste and, more particularly, to a container that utilizes an uneven aeration floor and reversing air flow direction.
2. Description of the Related Art
Composting is currently used as a method of recycling organic waste into a usable soil additive. As such, composting has been practiced for hundreds of years. However, several operational problems related to existing technology have limited the use of composting. Primarily, most composting apparatuses utilize poorly designed aeration systems that compost inefficiently and require expensive agitation equipment and buildings to prepare and compost the organic waste.
Expensive specialized equipment is usually required to handle and treat the organic waste as it goes through the preparatory stages, such as dewatering and batch mixing, and composting stages. During the preparatory treatment and composting, liquid and gaseous by-products are exposed to the environment causing nuisance odors and water pollution.
Most composting apparatuses use pressurized air to induce the flow of air through the compost. The pressurized air is generally introduced at the base of the compost pile through an air distribution system, such as an aeration floor. Air may be forced into the base of the pile causing an upward flow, or drawn out of the base of the pile causing a downward flow of air in the compost pile. The pressurized air may be activated or deactivated by several means including operator or automatic observation of time, temperature or oxygen levels.
Composting apparatuses generally use flat perforated floors or networks of orafices as the aeration floor. The floors are flat to allow loading equipment such as bucket loaders to remove the composted material from the composting system without obstruction from the floor. Flat perforated floors have major disadvantages. Pressurized air is distributed evenly over the entire surface of the floor. If less resistance is encountered adjacent to the side walls, then the air will "short circuit" up the side walls through the path of least resistance. The organic waste near the side walls will receive more air than the organic waste in the center of the container. The result is inefficient composting.
Research has shown that the use of pressurized air to control temperatures and provide oxygen during composting in apparatuses with flat aeration floors creates less than optimal conditions in a portion of the composting material. As shown in FIG. 5, research by Hiotink et all in 1985 showed that temperatures adjacent to the walls of an enclosed composting reactor were lower than temperatures at the center of the compost. In addition to cross-sectional variations in temperature, there were significant vertical variations in temperature based on the direction of air flow through the compost mass. The addition of pressurized air at the base of the compost mass cools the lower portion of the compost by evaporation of moisture in the compost. This evaporated moisture moves through the upper portion of the compost and condenses again releasing heat and moisture in the upper portion of the compost. The net result is the formation of temperature and moisture gradients in the direction of pressurized air flow. The gradients reduce the rate of composting in a portion of the composting material which is not at optimal temperatures or oxygen levels. If the pressurized air continues to move in one direction, the composting waste will remain cool and may dry to the point of ceasing microbial activity. Some systems try to overcome gradients by periodically agitating the composting material to homogenize the compost and thereby eliminate gradients. However, agtiation adds significant cost and complexity to such compost systems.
For the foregoing reasons, there is a need for an apparatus that composts efficiently but does not require relatively expensive agitation and acilllary equipment.